Development of investigative and diagnostic applications of the roentgen biplane videometry, roentgen videodensitometry, multiple projection roentgen reconstruction and related high-fidelity video scanning techniques is continuing. A major advance had been made over the past year in the ability to reconstruct the three-dimensional spatial distribution of roentgen opacity of the contents of the intact thorax, and especially of the heart. In particular, this capability now provides accurate three-dimensional information of the dynamic anatomy of the myocardium from which the length/tension relationship of the myocardium can be calculated for each 1/60th of a second during the cardiac cycle. These techniques are now being applied to provide detailed information of the pattern of ventricular filling and ejection under various conditions of ventricular filling pressure, peripheral arterial resistance, heart rate, and coronary blood flow. The measurement of the spatial location of lead beads placed in the lung parenchyma of dogs, and the simultaneously measured distribution of roentgen opacity, inhaled radioactive aerosol and radioactively labeled microspheres injected into the right ventricular outflow tract, will permit detailed correlation of pulmonary blood flow and ventilation throughout the lungs under various physiological conditions and magnitudes and directions of gravitational and inertial forces.